Many types of magnetic data storage media have been developed to store information. They include magnetic hard drives, magnetic diskettes, magnetic tapes, magnetic tape cartridges, hybrid magnetic media such as magnetic-optical disks, and the like. Increasing data storage density is a paramount goal in the development of new or improved types of magnetic data storage media. Reducing production costs is another goal.
Magnetic media generally function according to ferromagnetic principles. For example, the surface of a magnetic medium may be coated with one or more magnetic layers, e.g., in the form of a multi-layered magnetic stack or a magnetic alloy. The local magnetization of magnetic domains defined on the magnetic layers can be selectively oriented to encode data. The local magnetizations can then be detected and interpreted in order to read the recorded data. A hysteresis curve typically defines how the magnetic domains can be oriented or reoriented in response to application and removal of magnetic fields.
A number of techniques have been developed to increase storage densities and improve quality and reliability of magnetic media. For example, new and improved coatings have been developed in an effort to improve quality and performance of magnetic media. In addition, patterned, media have been developed, in which microscopic surface variations in the form of bumps, pits, ridges, grooves, or the like, are added to the media. The surface variations may be magnetically encoded, e.g., for the purpose of information storage, or to provide servo patterns that can be used to identify locations on the media with improved accuracy. In both cases, the addition of surface variations may increase storage densities.
Magnetic media can also be categorized as longitudinal or perpendicular. Most conventional magnetic media are longitudinal. In longitudinal media, magnetic anisotropy lies parallel to the plane of the medium. In other words, in longitudinal media, the magnetic orientation of individual magnetic domains is generally parallel to the surface of the medium.
In perpendicular media, on the other hand, magnetic anisotropy is perpendicular to the plane of the medium. In other words, in perpendicular media, the magnetic orientation of individual magnetic domains is perpendicular to the medium surface. Perpendicular media generally allow for higher storage densities than can be achieved in longitudinal media.